* Google Desktop
* Grepline / Cue (this is W10)
* ... various other products ...
I feel like for personal users, the product ultimately isn't sticky enough.
However, "enterprise search" feel more viable path especially this is where it becomes more valuable (and where the money is). Also anybody whose working at a large company would need to have some enterprise procurements to sign up for such a service anyway. I'm talking about players like Glean in this area.